Preventing Subtractive Track Separation

ABSTRACT

Disclosed are techniques for preventing extraction of original audio tracks from a song. The techniques are executed on a game platform and involve providing a first and second audio track representing parts of a musical composition, mixing the first audio track and the second audio track to provide a mixed audio track, generating an audio modification data comprising a series of substantially random audio modifiers, and then modifying, before playback, the mixed audio track based on the audio modification data to provide a modified mixed audio track, such that subtracting the second audio track from the modified mixed audio track produces a third audio track with an audibly detectable deviation from the first audio track.

FIELD OF THE INVENTION

The present invention relates generally to preventing subtractive trackseparation and, more specifically, to manipulating an audio track toprevent unwanted re-creation of the audio track.

BACKGROUND

Copyright infringement is a serious issue in the recording industry andamong musicians. What some consider “sampling,” others considerstealing. Yet sampling is a lucrative path to creating music. Theinfringer does not need to re-perform a sampled piece and does not needto pay others to recreate it. Naturally, musicians and record labelswish to protect their music from being sampled and re-used wholesale byinfringers.

In “music minus one” recordings, a mix of a song is provided minus onemusical part, e.g., a guitar track or a vocal track. Thesemusic-minus-one recordings are useful for training because the user canpractice the missing audio and have a full accompaniment that can berewound or replayed as often as necessary.

A danger of music-minus-one recordings is that if the music-minus-onerecording is “subtracted” from the original recording (with all partspresent), the “stem” (track) that represents the missing audio can berecreated. This will give the infringer a perfect copy of the missingtrack. This is especially an issue for recent rhythm-action gamesbecause they can, in theory, be music-minus-one recordings for eachpart—guitar, bass, vocals, and drums—as well as full recordings(assuming all parts are played perfectly).

A typical rhythm-action game mixes together individual stems duringgameplay. To make the experience immersive, the game can mute,attenuate, or otherwise alter a stem when the corresponding player'sperformance is imperfect. The game can also mix in additional sounds toindicate that a mistake was made. When a player provides the expectedinput at the expected time, however, their corresponding stem isunmuted, unattenuated, and otherwise unaltered in the final mix.

Selective muting or attenuation allows a potential infringer to derive aparticular audio track by playing the rhythm-action game first perfectly(so the whole ensemble is heard) and then again, but missing every note.If both performances are recorded, the all-misses recording can besubtracted from the all-perfect recording and the stem for that part canbe obtained. The following example illustrates this type of attack.

An example song is comprised of a stem audio track “X” and an additionalaudio track “A.” In some embodiments, A is the playback of allinstrument tracks except stem audio track X, while in other embodiments,A is the composite of several separate stem tracks, each representing aninstrument or combination of instruments. During a first play-through ofthe song, a player uses a video game controller to provide input thatmatches musical cues (known as gems) corresponding to stem audio trackX, such that the video game platform outputs audio that is an exactreproduction of the full ensemble in the original song, i.e., A+X.During a second play-through of the song, the player provides no inputto match the musical cues corresponding to stem audio track X, such thatthe video game platform outputs an audio track that is the full audio ofthe original song, but without the stem represented by stem audio trackX. Subtracting the audio output of the second play-through from theaudio of the first play-through results in the stem audio track X. Inother words, (A+X)−A=X. Using this technique, valuable stem tracks canbe stolen.

SUMMARY OF THE INVENTION

The present invention provides a way to prevent a player from obtainingan instrument track using a rhythm game.

In one aspect, the invention features, a method for preventing filteringof original audio tracks from a song executed on a computerized gameplatform. The method involves providing a first audio track representinga part of a musical composition, providing a second audio trackrepresenting at least one part of a musical composition, the at leastone part being different than the part represented by the first track,and mixing the first audio track and the second audio track to provide amixed audio track. The method also involves generating an audiomodification data comprising a series of substantially random audiomodifiers and modifying, before playback, the mixed audio track based onthe audio modification data to provide a modified mixed audio track,such that, subtracting the second audio track from the modified mixedaudio track produces a third audio track with an audibly detectabledeviation from the first audio track.

In some embodiments, the second audio track is randomized during asubsequent playback based on second audio modification data. In someembodiments, generating the audio modification data further comprisesdetermining the substantially random audio modifiers by setting thesubstantially random audio modifiers to a first value for a first randomtime interval and setting the substantially random audio modifiers to asecond value for a second random time interval.

In some embodiments, the first random time interval and the secondrandom time interval are between 1 and 2 seconds. In some embodiments,modifying the mixed audio track by the substantially random audiomodifiers changes pitch of the mixed audio track and the first valueproduces a positive 1.666 percent change in pitch and the second valueproduces a negative 1.666 percent change in pitch.

In some embodiments, modifying the mixed audio track comprises speedingup the mixed audio track or slowing down the mixed audio track based onthe substantially random audio modifiers. In some embodiments, themethod involves playing the output track. In some embodiments, thesubstantially random audio modifiers alter the mixed audio track suchthat the modification changes pitch of the mixed audio track. In someembodiments, the first audio track and the second audio track are guitartracks, bass tracks, vocal tracks, drum tracks, other musical instrumenttracks or any combination thereof.

In another aspect, the invention features a method executed on a gameplatform. The method involves providing a first audio track representinga part of a musical composition, providing a second audio trackrepresenting at least one part of a musical composition, the at leastone part being different than the part represented by the first track,and generating an audio modification track comprising a series ofsubstantially random audio modifiers. The method also involves mixingthe first audio track and the second audio track to provide a mixedaudio track and modifying, before playback, the mixed audio track basedon the audio modification track.

In another aspect, the invention features a method executed on a gameplatform. The method involves providing a first audio track representinga part of a musical composition, providing a second audio trackrepresenting at least one part of a musical composition, the at leastone part being different than the part represented by the first track,and mixing the first audio track and the second audio track to provide amixed audio track. The method also involves generating an audiomodification track comprising a series of substantially random audiomodifiers and modifying, before playback, the mixed audio track based onthe audio modification track.

In another aspect, the invention features a method executed on a gameplatform. The method involves providing a first audio track representinga part of a musical composition, providing a second audio trackrepresenting at least one part of a musical composition, the at leastone part being different than the part represented by the first track,and generating an audio modification track comprising a first series ofsubstantially random audio modifiers. The invention also involvesmodifying, before playback, the first audio track based on the audiomodification track, modifying, before playback, the second audio trackbased on the audio modification track, and mixing the modified firstaudio track and the modified second audio track to provide a mixed audiotrack for playback.

In another aspect, the invention features a method for preventingfiltering of original audio tracks from a song executed on acomputerized game platform. The method involves providing a first audiotrack representing a part of a musical composition, providing a secondaudio track representing at least one part of a musical composition, theat least one part being different than the part represented by the firsttrack, and generating an audio modification track comprising a series ofsubstantially random audio modifiers. The method also involves mixingthe first audio track and the second audio track to provide a mixedaudio track and modifying, before playback, the mixed audio track basedon the audio modification track to provide a modified mixed audio track,such that, subtracting the second audio track from the modified mixedaudio track produces a third audio track with an audibly detectabledeviation from the first audio track.

In another aspect, the invention features a computer program product,tangibly embodied in a computer-readable medium, for preventingfiltering of original audio tracks from a song. The computer programproduct includes an executable instruction operable to cause a gameplatform to provide two or more original audio tracks, mix the two ormore original audio tracks to provide a mixed audio track, and generatean audio modification track comprising a series of substantially randomaudio modifiers. The executable instructions are also operable to causethe game platform to modify, before playback, the mixed audio trackbased on the audio modification track to provide a modified mixed audiotrack, such that, subtracting the second audio track from the modifiedmixed audio track produces a third audio track with an audiblydetectable deviation from the first audio track.

In another aspect, the invention features a computer program product,tangibly embodied in a computer-readable medium, for preventingfiltering of original audio tracks from a song. The computer programproduct including executable instruction operable to cause a gameplatform provide a first audio track representing a part of a musicalcomposition, provide a second audio track representing at least one partof a musical composition, the at least one part being different than thepart represented by the first track, and generate an audio modificationtrack comprising a first series of substantially random audio modifiers.The executable instruction is also operable to cause a game platform tomodify, before playback, the first audio track based on the audiomodification track, modify, before playback, the second audio trackbased on the audio modification track, and mix the modified first audiotrack and the modified second audio track to provide a mixed audio trackfor playback.

In another aspect, the invention features a computer program product,tangibly embodied in a computer-readable medium, for preventingfiltering of original audio tracks from a song. The computer programproduct including executable instruction operable to cause a gameplatform to provide a first audio track representing a part of a musicalcomposition, provide a second audio track representing at least one partof a musical composition, the at least one part being different than thepart represented by the first track, and generate an audio modificationtrack comprising a series of substantially random audio modifiers. Theexecutable instruction is also operable to cause a game platform to mixthe first audio track and the second audio track to provide a mixedaudio track and modify, before playback, the mixed audio track based onthe audio modification track to provide a modified mixed audio track,such that, subtracting the second audio track from the modified mixedaudio track produces a third audio track with an audibly detectabledeviation from the first audio track.

Advantages of the invention include that the audio that is output in thecase of a flawless performance is as close as possible to the originalrecording, that the audio that is output in the case of an imperfectperformance is as close as possible to the original recording withoutthe corresponding instrument, and that the stem tracks are preventedfrom being stolen.

Other aspects and advantages of the present invention will becomeapparent from the following detailed description, taken in conjunctionwith the accompanying drawings, illustrating the principles of theinvention by way of example only.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of the presentinvention, as well as the invention itself, will be more fullyunderstood from the following description of various embodiments, whenread together with the accompanying drawings, in which:

FIG. 1 is a diagram of a system for playing a rhythm-action game;

FIG. 2 is multiple graphs of stems for various song parts;

FIG. 3 is a block diagram of an exemplary video game platform;

FIG. 4 is a flow chart of a method for preventing filtering of originalaudio tracks from a song executed on a computerized game platform;

FIG. 5A illustrates an audio track A;

FIG. 5B illustrates an audio track X;

FIG. 5C illustrates a mixed audio track A+X;

FIG. 6A illustrates a random data stream R1, which indicates a series ofvery small pitch shift percentages;

FIG. 6B illustrates track A mixed with track X and randomized by randomdata stream R1;

FIG. 7A illustrates a random data stream R2, which indicates a series ofvery small pitch shift percentages different from R1;

FIG. 7B illustrates track A where the pitch is randomized by random datastream R2;

FIG. 8A illustrates a result of an attempt to extract track X bysubtracting track A randomized by the random data stream R2 from thecombination of track A mixed with track X randomized by random datastream R1;

FIG. 8B illustrates a deviation of the result of the subtraction in FIG.8A from the original track X, which is audible as phasing artifactsoverlaid on track X.

DETAILED DESCRIPTION

FIG. 1 is a diagram depicting a game platform 100 for running gamesoftware and various components in signal communication with the gameplatform. Each player may use a game platform 100 in order toparticipate in the game. In one embodiment, the game platform 100 is adedicated game console, such as: PLAYSTATION® 2, PLAYSTATION® 3, or PSP®manufactured by Sony Corporation; WII™, NINTENDO DSO, NINTENDO DSi™, orNINTENDO DS LITE™ manufactured by Nintendo Corp.; or XBOX® or XBOX 360®manufactured by Microsoft Corp. In other embodiments, the game platform100 comprises a personal computer, personal digital assistant, orcellular telephone. Throughout the specification and claims, wherereference is made to “the game platform 100” performing a function,“game platform 100” may, for some implementations, be read as “gameplatform 100 with game software executing on it.” References to the gameplatform 100 and omission of reference to the game software does notimply absence of the game software. Game software alone may also embodythe invention, e.g., a computer program product, tangibly embodied in acomputer-readable storage medium, while in some embodiments theinvention is implemented purely in hardware such as a computer processorconfigured to perform specific functions. In other embodiments theinvention is embodied by a combination of hardware and software.

The game platform 100 is typically in electrical and/or signalcommunication with a display 105, e.g., via an HDMI cable. This may be atelevision, an LCD monitor, projector, or the like. The game platform isalso typically in electrical or signal communication with one or morecontrollers or input devices. In FIG. 1, the game platform 100 is insignal communication with a one or more microphones 110, a firstsimulated guitar controller 115 a, a second simulated guitar controller115 b (guitar controllers, collectively, 115), and one or more drumperipherals 117. Other inputs can be other simulated instruments such askeyboards (not shown), standard controllers for the respective gameplatforms, and/or keyboards and/or mice (also not shown). Microphones,controllers, etc. may be connected via a physical wire, e.g., via a USBconnection, or may be connected wirelessly, e.g., via Bluetooth, FM, aproprietary wireless protocol used by the Microsoft Xbox 360 gameconsole, or other wireless signaling protocols.

Though reference is made to the game platform 100 generally, the gameplatform, in some embodiments, contains hardware and/or software thatperform general or specific tasks, such as a central processing unit, aninstrument analysis module, a singing analysis module, a soundprocessing module that provides sound output, e.g., to a speaker, astorage device, Random Access Memory, Read Only Memory, peripheralinterfaces, networking interface, media interfaces (e.g., a CD-ROM, DVD,or Blu-Ray drive or SD, Compact Flash, or other memory formatinterfaces), graphic processors and others. Each module may also containsub-modules. For example the singing analysis module may contain a dataextractor module, a digital signal processor module, a comparisonmodule, and a performance evaluation module (not shown). Alternatively,in software implementations of the modules, modules or combinations ofmodules may reside within the RAM or ROM (and/or be loaded into thesefrom media via the media interface or from storage) for execution by thecentral processing unit.

In some embodiments, execution of game software limits the game platform100 to a particular purpose, e.g., playing the particular game. In thesescenarios, the game platform 100 combined with the software, in effect,becomes a particular machine while the software is executing. In someembodiments, though other tasks may be performed while the software isrunning, execution of the software still limits the game platform 100and may negatively impact performance of the other tasks. While the gamesoftware is executing, the game platform directs output related to theexecution of the game software to the display 105, thereby controllingthe operation of the display. The game platform 100 also can receiveinputs provided by one or more players, perform operations andcalculations on those inputs, and direct the display to depict arepresentation of the inputs received and other data such as resultsfrom the operations and calculations, thereby transforming the inputreceived from the players into a visual representation of the inputand/or the visual representation of an effect caused by the player.

In some embodiments, the processor reads song data from a MIDI-likefile. MIDI tracks in the file dictate information for specificinstruments or game objects, such as cameras or scene information. TheMIDI “notes” in the tracks are indicators for song data, gem placementinformation, avatar action cues, camera cuts, cues for events on stage,and other game events. Although the MIDI file uses MIDI note numbers,these MIDI notes do not typically correspond to actual note or pitchinformation.

The audio data for a song in rhythm-action games usually comprisesseveral separate audio tracks known as “stems.” The stems are derivedfrom the master audio tracks of an original song recording. These areoften the same master audio tracks that are mixed together to produce afinal audio stereo mix heard in the published version of a song (on aCD, for example). Typically, there is at least one stem for eachplayable part of the song.

FIG. 2 shows graphs 200 of stems for various parts of a song, e.g., astem 220 for a guitar part of the song, a stem 240 for a drum part ofthe song, a stem 260 for a vocal part of the song, and a stem 280 for abass part of the song. Additional musical parts may be used as well,depending on the song, e.g., some songs also have keyboard parts. Duringgameplay, stems corresponding to each part that players have selected toplay (selectively altered depending on each players' respectiveperformance), stems corresponding to the parts that are not being playedby the players, and background music and sounds are dynamically mixedtogether. The dynamic mixing produces the final audio—a combination ofbackground music, stems corresponding to non-player-selected parts, andthe stems corresponding to parts being played by players—heard duringgameplay. Dynamic mixing allows the game to affect the sound of thewhole song based on the users' input. For example, a part may beattenuated or muted when a player is not playing his or her partcorrectly. Additionally or alternatively, effects such as pitch-bendingcan be added to a particular stem based on input from a player.Additional sounds not present in the original recording may also beadded, e.g., a “miss” sound when the player does not play his or herpart correctly. These all make the simulated musical experience moreauthentic and immersive.

FIG. 3 is a block diagram 300 of some internal components of anexemplary video game platform 305. During gameplay, one or more inputsignals are received by the video game platform 305 via one or moreports 310 a, 310 b, 310 n, generally 310. As described above, the inputsignals correspond to buttons pushed on video game controllers or inputactions provided by one or more players during gameplay. Not all portsnecessarily receive input at the same time—input varies with the numberof instrument/game controllers present and the number of playersplaying. The ports 310 are configured to receive input from any of aguitar video game controller, a microphone, a bass video gamecontroller, a drum video game controller, a musical instrument videogame controller, or any combination thereof.

The input signals 315 a, 315 b, . . . , 315 n, generally 315, are inputto a processor 317. During gameplay, the processor 317 loads andcontrols the playback of stems, background, and sound effects retrievedfrom an audio signal storage device 320. The storage device 320 can bean optical disc, a hard drive, a flash drive, or it can be random accessmemory or read only memory of the game platform 305. During gameplay,the processor 317 determines if the players' input signals 315 coincidewith the expected inputs retrieved from game data storage 322 at thecorrect times (game data storage 322 may be a separate device from theaudio signal storage 320, or, in some embodiments, on the same medium asthe audio signal storage 320). The processor 317 then controls whichaudio signals 325 a, 325 b, . . . , 325 n are input to the mixer 330. Insome embodiments, the mixer 330 is implemented as part of the processor317. For example, if during gameplay a player performs his or her partcorrectly, that is, the player presses the correct buttons and correctlystrums on a video game controller at the correct time throughout thesong, then the audio track that is fed to the mixer for thatinstrument—over the course of the song—is the entire stem for thatinstrument. However, if during gameplay a player does not play his orher part correctly, e.g., doesn't strum at the indicated time, or strumswhile pressing a button other than the indicated button, or strums atthe wrong time with the proper button pressed, the processor 317 mutesor affects the audio track for that instrument as that audio stream isfed to the mixer. This results in a fragmented performance of thatparticular part, and correspondingly the song as a whole.

Once the mixer 330 receives the audio from the processor 317, the mixer330 mixes the output audio tracks to produce a mixed audio track. In oneembodiment, the mixer produces a weighted sum of input audio tracks. Invarious embodiments, the audio is input to an equalizer, a compressor, alimiter and/or any other audio pipeline components.

The mixed audio track is input 335 to a pitch shifter 347. A random datastream generator 340 generates a random data stream 342. The random datastream 342 is input to the pitch shifter 347. The pitch shifter 347resamples the mixed audio track 335 according to the resampling ratioprovided by the random data stream 342 to produce a randomized mixedaudio track 345. In some embodiments, the random data stream 342 is aseries of percentages that indicate the percentage a pitch of the mixedaudio track input 335 is shifted relative to its original sample rate.In some embodiments, the random data stream 342 is a series ofpercentages that indicate the percentage a pitch of the mixed audiotrack input 335 is shifted relative to its current resampling ratio.Typically the effect of applying the randomized data stream to the mixedtrack results in a difference that is undetectable to the human ear.

The randomized mixed audio track 345 is then output to a speaker oraudio out port 350 of the video game platform 305 for playback to theplayer. A benefit of the randomized mixed audio track is evident duringsubsequent play-throughs of the game. With each play-through of thesong, the final audio is slightly different. When a subtraction attemptis made, the randomized audio that is different between the finaloutputs creates artifacts that make the resulting stems unusable. Insome embodiments, the artifacts sound like irregular flanging effects.The process is explained in more detail below.

FIG. 4 is a flow chart 400 describing one technique for preventingfiltering of original audio tracks from a song executed on acomputerized game platform. The method begins by receiving (Step 410) arequest for a first audio track. The first audio track (shown in FIG.5A) is an audio track “A” belonging to a song that has at least twoaudio tracks, and, in some embodiments, the audio track has both a leftaudio track component and a right audio track component, i.e., the audiotrack is a stereo pair. The method also includes receiving (Step 420) arequest for a second audio track. The second audio track (shown in FIG.5B) is an audio track belonging to the song, separate from track A. Thesecond audio track will be referred to as track “X”.

The first audio track and the second audio track are then mixed (Step430), e.g., by a mixer 330, to provide a mixed audio track, shown inFIG. 5C as A+X. As discussed above, during perfect gameplay, the mixedaudio track is a reproduction of the full song. In some embodiments, thesong is composed of multiple audio tracks, either corresponding to partsthat are playable by other players, or corresponding to parts that areplayable by the same player on multiple instruments simultaneously, orcorresponding to parts that are unplayable background music, and thusmultiple audio tracks beyond A and X are mixed during Step 430.

Then, audio modification data is generated (Step 440), typically by arandom data stream generator 340. FIG. 6A shows an exemplary audiomodification data “R1.” In some embodiments, the audio modification datais generated by generating a new random number for a specified durationof the audio track. In some embodiments, the random numbers generatedare based on a seed value, s, such that the sequence of numbersgenerated based on the same seed is always the same, but the sequence ofnumbers generated based on a different seed is always different.

Then, the mixed audio track is modified (Step 450) based on the audiomodification data. FIG. 6B illustrates the mixed audio track A+Xas-modified by applying audio modification data R1. In some embodiments,the random data stream controls a resampling ratio. The resampling ratiocan cause the pitch of the mixed audio track to be altered slightly. Insome embodiments, the random data stream controls a timer which causesswitching among pre-determined resampling ratios. In some of thoseembodiments, a predetermined resampling ratio can exclude 1.0, such thatthe playback is never at its original rate. In some embodiments, thepitch shift is accomplished using resampling and interpolation,producing a non-frequency-preserving and/or non-time-preserving pitchshift. Then the modified mixed audio track is provided (Step 460) forplayback by the video game platform.

In some embodiments, the random data stream generator is implemented asfollows. A random number generator with a seed of s generates a timedelay value in the range of 1 to 2 seconds, although other time rangesare also possible. In some embodiments, the time delay values are drawnfrom a pre-determined set of possible values. In some embodiments, thetime delay values are selected in a pre-determined pattern. For theduration of the period determined by the time delay value, the valueproduced by the random stream generator is a specific value. In someembodiments, this value represents a resampling ratio that is used toalter the pitch of a signal. In some embodiments, the resampling ratiois in the range of −1.666% to +1.666%. In some embodiments, theresampling ratio is never 0%. The values produced by the random streamgenerator can be random and/or drawn from a pre-determined set ofvalues. For example, the random stream generator can generate only−1.666% or +1.666%, and no other values. In another example, the randomstream generator can generate any value between −1.666% or +1.666%. Inanother example, the random stream generator can generate only −1.666%or +1.666% for a first duration and then generate any value between−1.666% or +1.666%. In some embodiments, the random stream generator cangenerate any value. In some embodiments, a pattern of values produced bythe random stream generator can be random, or it can be pre-determined,for example, alternating between increased and decreased pitch. Afterthe specified time expires, a new time delay value can be generated.

In the most sensitive band of human hearing, between 1 KHz and 2 KHz,the threshold for perceiving a pitch shift is approximately 4 to 5percent. In some embodiments, the resampling ratio is modified bypositive or negative 1.666%, so as to be below the level of humanperception. In some embodiments, the random stream generator produces analternating series of values such that the pitch alternates betweenbeing shifted +1.666% and −1.666% of the normal pitch, and varies atrandom intervals between 1 and 2 seconds.

In some embodiments, the random data stream is applied to the firstaudio track and the second audio track before mixing the first audiotrack with the second audio track. In these embodiments, the same randomseed may be used to produce identical random data streams for the audiotracks. In some embodiments, the first audio track and the second audiotrack are mixed to produce a mixed audio track, and then the random datastream is applied to the mixed audio track.

The audio tracks are not always limited to tracks or audio from a singleinstrument. For example, in some embodiments, the first audio trackincludes an audio data from a first musical instrument and partial audiodata from a second musical instrument. For example, when a vocal partand a guitar part are performed and recorded at the same time, part ofthe vocals may “bleed” into the guitar audio track and some of theguitar part will “bleed” into the vocal audio track.

The benefit of the technique described herein is that when the audiomodification data is applied to a mixed audio track, it is undetectableby the human ear. Upon a second playback of the mixed audio track, theaudio modification data produces a deviation from the first playback ofthe mixed audio track sufficient to make isolation of an original audiotrack impossible. For example, assume a discrete first audio track A(t)and a discrete second audio track X(t) containing stem audio data with asample rate of 44 KHz. The discrete first audio track A(t) and thediscrete second audio track X(t) can be samples of a continuous audiotrack. Also assume a discrete random data stream R(t,s1), where s1 is arandom seed and where the sample rate is the same as for A(t) and X(t).The discrete random data stream R(t,s1) includes resampling ratios, asdescribed above, that vary the pitch of a signal. The techniques used toapply the resampling ratio to the signal are known in the art, thus arenot further discussed here. For the first play-through, assume a perfectperformance by the player, resulting in an uninterrupted X(t) output.After resampling and mixing (or mixing and resampling), the resultingaudio output is nearly indistinguishable from a standard stereo mix.

The random data stream R(t,s) can use a different seed for eachplay-through. In the second play-through, assume that s2 is used as theseed, so R(t,s2) produces a different series of resampling ratios thanR(t,s1). In this performance, the player misses all of the cuescorresponding to the stem X(t). Thus, X(t) is not present in the finalmix. After resampling and mixing (or mixing and resampling), the secondplay-through is nearly indistinguishable from a music-minus-onerecording, with the instrument corresponding to X(t) not present. Whensubtracting the second performance from the first performance, however,the result is close to X(t), but has significant and very perceptibleflanging artifacts. In some embodiments, X(t) is not randomized duringthe second playback. In these embodiments, subtracting the secondplayback from the first playback also yields very perceptible flangingartifacts.

The above-described techniques can be implemented in digital electroniccircuitry, or in computer hardware, firmware, software, or incombinations of them. The implementation can be as a computerized methodor process, or a computer program product, i.e., a computer programtangibly embodied in a machine-readable storage device, for executionby, or to control the operation of, data processing apparatus, e.g., aprogrammable processor, a computer, a game console, or multiplecomputers or game consoles. A computer program can be written in anyform of programming language, including compiled or interpretedlanguages, and it can be deployed in any form, including as astand-alone program or as a module, component, subroutine, or other unitsuitable for use in a computing environment. A computer program can bedeployed to be executed on one computer or game console or on multiplecomputers or game consoles at one site or distributed across multiplesites and interconnected by a communication network.

Method steps can be performed by one or more programmable processorsexecuting a computer or game program to perform functions of theinvention by operating on input data and generating output. Method stepscan also be performed by, and apparatus can be implemented as a gameplatform such as a dedicated game console, e.g., PLAYSTATION® 2,PLAYSTATION® 3, or PSP® manufactured by Sony Corporation; WII™, NINTENDODSC, NINTENDO DSi™, NINTENDO DSi XL™ or NINTENDO DS LITE™ manufacturedby Nintendo Corp.; or XBOX® or XBOX 360® manufactured by Microsoft Corp.or special purpose logic circuitry, e.g., an FPGA (field programmablegate array) or an ASIC (application-specific integrated circuit) orother specialized circuit. Modules can refer to portions of the computeror game program and/or the processor/special circuitry that implementsthat functionality.

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer or gameconsole. Generally, a processor receives instructions and data from aread-only memory or a random access memory or both. The essentialelements of a computer or game console are a processor for executinginstructions and one or more memory devices for storing instructions anddata. Generally, a computer also includes, or be operatively coupled toreceive data from or transfer data to, or both, one or more mass storagedevices for storing data, e.g., magnetic, magneto-optical disks, oroptical disks. Data transmission and instructions can also occur over acommunications network. Information carriers suitable for embodyingcomputer program instructions and data include all forms of non-volatilememory, including by way of example semiconductor memory devices, e.g.,EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internalhard disks or removable disks; magneto-optical disks; and CD-ROM andDVD-ROM disks. The processor and the memory can be supplemented by, orincorporated in special purpose logic circuitry.

To provide for interaction with a player, the above described techniquescan be implemented on a computer or game console having a displaydevice, e.g., a CRT (cathode ray tube) or LCD (liquid crystal display)monitor, a television, or an integrated display, e.g., the display of aPSP® or Nintendo DS. The display can in some instances also be an inputdevice such as a touch screen. Other typical inputs include simulatedinstruments, microphones, or game controllers. Alternatively input canbe provided by a keyboard and a pointing device, e.g., a mouse or atrackball, by which the player can provide input to the computer or gameconsole. Other kinds of devices can be used to provide for interactionwith a player as well; for example, feedback provided to the player canbe any form of sensory feedback, e.g., visual feedback, auditoryfeedback, or tactile feedback; and input from the player can be receivedin any form, including acoustic, speech, or tactile input.

The above described techniques can be implemented in a distributedcomputing system that includes a back-end component, e.g., as a dataserver, and/or a middleware component, e.g., an application server,and/or a front-end component, e.g., a client computer or game consolehaving a graphical player interface through which a player can interactwith an example implementation, or any combination of such back-end,middleware, or front-end components. The components of the system can beinterconnected by any form or medium of digital data communication,e.g., a communication network. Examples of communication networksinclude a local area network (“LAN”) and a wide area network (“WAN”),e.g., the Internet, and include both wired and wireless networks.

The computing/gaming system can include clients and servers or hosts. Aclient and server (or host) are generally remote from each other andtypically interact through a communication network. The relationship ofclient and server arises by virtue of computer programs running on therespective computers and having a client-server relationship to eachother.

The invention has been described in terms of particular embodiments. Thealternatives described herein are examples for illustration only and notto limit the alternatives in any way. The steps of the invention can beperformed in a different order and still achieve desirable results. Someaspects of the inventions described herein are reflected in thefollowing claims, but the inventions are not limited to these.Specifically there are apparatuses configured to carry of the steps ofthe following methods, apparatuses whose components embody the claimelements below and there are computer program products, tangibleembodied in a computer-readable storage medium, which includesinstructions operable to cause a data processing apparatus to performthe following methods.

What is claimed is:
 1. A method for preventing filtering of originalaudio tracks from a song executed on a computerized game platformcomprising: providing a first audio track representing a part of amusical composition; providing a second audio track representing atleast one part of a musical composition, the at least one part beingdifferent than the part represented by the first track; mixing the firstaudio track and the second audio track to provide a mixed audio track;generating an audio modification data comprising a series ofsubstantially random audio modifiers; and modifying, before playback,the mixed audio track based on the audio modification data to provide amodified mixed audio track, such that, subtracting the second audiotrack from the modified mixed audio track produces a third audio trackwith an audibly detectable deviation from the first audio track.
 2. Themethod of claim 1 wherein the second audio track is randomized during asubsequent playback based on second audio modification data.
 3. Themethod of claim 1 wherein generating the audio modification data furthercomprises determining the substantially random audio modifiers bysetting the substantially random audio modifiers to a first value for afirst random time interval and setting the substantially random audiomodifiers to a second value for a second random time interval.
 4. Themethod of claim 3 wherein the first random time interval and the secondrandom time interval are between 1 and 2 seconds.
 5. The method of claim3 wherein modifying the mixed audio track by the substantially randomaudio modifiers changes pitch of the mixed audio track and the firstvalue produces a positive 1.666 percent change in pitch and the secondvalue produces a negative 1.666 percent change in pitch.
 6. The methodof claim 1 wherein modifying the mixed audio track comprises speeding upthe mixed audio track or slowing down the mixed audio track based on thesubstantially random audio modifiers.
 7. The method of claim 1 furthercomprising playing the output track.
 8. The method of claim 1 whereinthe substantially random audio modifiers alter the mixed audio tracksuch that the modification changes pitch of the mixed audio track. 9.The method of claim 1 wherein the first audio track and the second audiotrack are guitar tracks, bass tracks, vocal tracks, drum tracks, othermusical instrument tracks or any combination thereof.
 10. A methodexecuted on a game platform comprising: providing a first audio trackrepresenting a part of a musical composition; providing a second audiotrack representing at least one part of a musical composition, the atleast one part being different than the part represented by the firsttrack; generating an audio modification track comprising a series ofsubstantially random audio modifiers; mixing the first audio track andthe second audio track to provide a mixed audio track; and modifying,before playback, the mixed audio track based on the audio modificationtrack.
 11. A method executed on a game platform comprising: providing afirst audio track representing a part of a musical composition;providing a second audio track representing at least one part of amusical composition, the at least one part being different than the partrepresented by the first track; mixing the first audio track and thesecond audio track to provide a mixed audio track; generating an audiomodification track comprising a series of substantially random audiomodifiers; and modifying, before playback, the mixed audio track basedon the audio modification track.
 12. A method executed on a gameplatform comprising: providing a first audio track representing a partof a musical composition; providing a second audio track representing atleast one part of a musical composition, the at least one part beingdifferent than the part represented by the first track; generating anaudio modification track comprising a first series of substantiallyrandom audio modifiers; modifying, before playback, the first audiotrack based on the audio modification track; modifying, before playback,the second audio track based on the audio modification track; and mixingthe modified first audio track and the modified second audio track toprovide a mixed audio track for playback.
 13. A method for preventingfiltering of original audio tracks from a song executed on acomputerized game platform comprising: providing a first audio trackrepresenting a part of a musical composition; providing a second audiotrack representing at least one part of a musical composition, the atleast one part being different than the part represented by the firsttrack; generating an audio modification track comprising a series ofsubstantially random audio modifiers; mixing the first audio track andthe second audio track to provide a mixed audio track; and modifying,before playback, the mixed audio track based on the audio modificationtrack to provide a modified mixed audio track, such that, subtractingthe second audio track from the modified mixed audio track produces athird audio track with an audibly detectable deviation from the firstaudio track.
 14. A computer program product, tangibly embodied in acomputer-readable medium, for preventing filtering of original audiotracks from a song, the computer program product including executableinstruction operable to cause a game platform to: provide two or moreoriginal audio tracks; mix the two or more original audio tracks toprovide a mixed audio track; generate an audio modification trackcomprising a series of substantially random audio modifiers; and modify,before playback, the mixed audio track based on the audio modificationtrack to provide a modified mixed audio track, such that, subtractingthe second audio track from the modified mixed audio track produces athird audio track with an audibly detectable deviation from the firstaudio track.
 15. A computer program product, tangibly embodied in acomputer-readable medium, for preventing filtering of original audiotracks from a song, the computer program product including executableinstruction operable to cause a game platform to: provide a first audiotrack representing a part of a musical composition; provide a secondaudio track representing at least one part of a musical composition, theat least one part being different than the part represented by the firsttrack; generate an audio modification track comprising a first series ofsubstantially random audio modifiers; modify, before playback, the firstaudio track based on the audio modification track; modify, beforeplayback, the second audio track based on the audio modification track;and mix the modified first audio track and the modified second audiotrack to provide a mixed audio track for playback.
 16. A computerprogram product, tangibly embodied in a computer-readable medium, forpreventing filtering of original audio tracks from a song, the computerprogram product including executable instruction operable to cause agame platform to: provide a first audio track representing a part of amusical composition; provide a second audio track representing at leastone part of a musical composition, the at least one part being differentthan the part represented by the first track; generate an audiomodification track comprising a series of substantially random audiomodifiers; mix the first audio track and the second audio track toprovide a mixed audio track; and modify, before playback, the mixedaudio track based on the audio modification track to provide a modifiedmixed audio track, such that, subtracting the second audio track fromthe modified mixed audio track produces a third audio track with anaudibly detectable deviation from the first audio track.